We have recently initiated studies to determine the origin and immunologic function of a neoplastic cell line obtained from a patient with Hodgkin's disease. Initial characterization of this cell line demonstrates that it is a potent stimulator of the human primary mixed lymphocyte response. This MLC stimulation is totally blocked by a monoclonal anti-Ia antibody and occurs despite the absence of detectable interleukin 1 production by the cell line. The cell line is also capable of serving as an accessory cell for the proliferative response of purified T cells to mitogens. In this regard and in its cell surface characteristics, these tumor cells resemble the murine dendritic cells. Patients with Hodgkin's disease have certain immunologic abnormalities that return to normal when they are cured such as delayed hypersensitivity skin test reactivity and prostaglandin mediated suppression of proliferative responses. In contrast, other immunologic abnormalities such as the increased sensitivity to monocyte or T cell suppressor cells remains persistently depressed independent of treatment. These abnormalities may be related to a patient's genetic predisposition to develop Hodgkin's disease. Patients with untreated non-Hodgkin's lymphomas have diminished proliferative responses to pokeweed mitogen due to deficient helper T cell function. Monoclonal antibody studies reveal that the helper T cells are phenotypically present but functionally impaired. In addition, patients with non-Hodgkin's lymphoma have depressed antibody production as well. Of interest, both B and T cell non-Hodgkin's lymphomas can respond clinically to treatment with a nonspecific anti-lymphocyte serum. The role of immunoregulatory abnormalities in the pathogenesis and biology of the non-Hodgkin's lymphoma is being investigated further. A murine model of ovarian cancer can be successfully treated by nonspecific immunotherapy in the absence of a cellular immune response against the tumor. The lack of cellular immune response is explained by the tumor's lack of H-2 antigens. Interperitoneal chemotherapy and immunotherapy are synergistic in the treatment of this tumor.